From: Roman Gushchin guro@fb.com
The lowest bit in page->memcg_data is used to distinguish between struct memory_cgroup pointer and a pointer to a objcgs array. All checks and modifications of this bit are open-coded.
Let's formalize it using page memcg flags, defined in enum page_memcg_data_flags.
Additional flags might be added later.
Signed-off-by: Roman Gushchin guro@fb.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Alexei Starovoitov ast@kernel.org Reviewed-by: Shakeel Butt shakeelb@google.com Acked-by: Johannes Weiner hannes@cmpxchg.org Acked-by: Michal Hocko mhocko@suse.com Link: https://lkml.kernel.org/r/20201027001657.3398190-4-guro@fb.com Link: https://lore.kernel.org/bpf/20201201215900.3569844-4-guro@fb.com Signed-off-by: Chen Huang chenhuang5@huawei.com --- include/linux/memcontrol.h | 32 ++++++++++++++++++++------------ 1 file changed, 20 insertions(+), 12 deletions(-)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 2805fe81f97d..4a0feb9d4b82 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -343,6 +343,15 @@ struct mem_cgroup {
extern struct mem_cgroup *root_mem_cgroup;
+enum page_memcg_data_flags { + /* page->memcg_data is a pointer to an objcgs vector */ + MEMCG_DATA_OBJCGS = (1UL << 0), + /* the next bit after the last actual flag */ + __NR_MEMCG_DATA_FLAGS = (1UL << 1), +}; + +#define MEMCG_DATA_FLAGS_MASK (__NR_MEMCG_DATA_FLAGS - 1) + /* * page_memcg - get the memory cgroup associated with a page * @page: a pointer to the page struct @@ -404,13 +413,7 @@ static inline struct mem_cgroup *page_memcg_check(struct page *page) */ unsigned long memcg_data = READ_ONCE(page->memcg_data);
- /* - * The lowest bit set means that memcg isn't a valid - * memcg pointer, but a obj_cgroups pointer. - * In this case the page is shared and doesn't belong - * to any specific memory cgroup. - */ - if (memcg_data & 0x1UL) + if (memcg_data & MEMCG_DATA_OBJCGS) return NULL;
return (struct mem_cgroup *)memcg_data; @@ -429,7 +432,11 @@ static inline struct mem_cgroup *page_memcg_check(struct page *page) */ static inline struct obj_cgroup **page_objcgs(struct page *page) { - return (struct obj_cgroup **)(READ_ONCE(page->memcg_data) & ~0x1UL); + unsigned long memcg_data = READ_ONCE(page->memcg_data); + + VM_BUG_ON_PAGE(memcg_data && !(memcg_data & MEMCG_DATA_OBJCGS), page); + + return (struct obj_cgroup **)(memcg_data & ~MEMCG_DATA_FLAGS_MASK); }
/* @@ -444,10 +451,10 @@ static inline struct obj_cgroup **page_objcgs_check(struct page *page) { unsigned long memcg_data = READ_ONCE(page->memcg_data);
- if (memcg_data && (memcg_data & 0x1UL)) - return (struct obj_cgroup **)(memcg_data & ~0x1UL); + if (!memcg_data || !(memcg_data & MEMCG_DATA_OBJCGS)) + return NULL;
- return NULL; + return (struct obj_cgroup **)(memcg_data & ~MEMCG_DATA_FLAGS_MASK); }
/* @@ -460,7 +467,8 @@ static inline struct obj_cgroup **page_objcgs_check(struct page *page) static inline bool set_page_objcgs(struct page *page, struct obj_cgroup **objcgs) { - return !cmpxchg(&page->memcg_data, 0, (unsigned long)objcgs | 0x1UL); + return !cmpxchg(&page->memcg_data, 0, (unsigned long)objcgs | + MEMCG_DATA_OBJCGS); } #else static inline struct obj_cgroup **page_objcgs(struct page *page)